Fuel cells have been proposed as a power source for a variety of applications, including electrical vehicular power plants replacing internal combustion engines. In proton exchange member (PEM) type fuel cells, hydrogen is supplied to an anode of the fuel cell and oxygen is supplied as an oxidant to the cathode of the fuel cell. The resultant electricity can be utilized to run an electric motor or for other purposes depending upon the ultimate use of the fuel cell system.
For vehicular and other applications, it may be desirable to use a liquid fuel, such as gasoline, diesel, methanol and the like, as a source of hydrogen for the fuel cell if hydrogen is not an available fuel. Such liquid fuels must be dissociated or reformed by releasing the hydrogen content thereof. The dissociation reaction is generally accomplished in a fuel processor that may include a series of reactors, including an autothermal reformer or a steam reformer as the primary reactor. For many reactor systems, especially for those in mobile applications, a fast start time requiring minimal energy is important. One significant aspect of start time includes the time that it takes to reach catalyst “light-off” or activation temperatures. Many current techniques for quick heatup of catalysts depend upon heating the entire reactor bed. Some current methods of heating the catalyst include resistive heating of the catalyst support (EHC), exposing the reactor bed to hot reformate gas, or by generating heat via reformate oxidation. However, these methods generally operate by non-selective heating of the entire reactor system including the entire mass of the reactor bed, which potentially results in energy lost by heat dissipation from the catalytically active sites and by heating the bulk of the reactor, consequently resulting in longer times to reach start-up temperature. For example, reformate oxidation entails adding air to chemically react with the reducing gas entering the catalyst bed, which generally provides a relatively fast heating of the catalyst to activation temperatures. However, in addition to non-selective heating of the reactor bed, the heat distribution is often not uniform throughout the entire reactor and bed, generally because the front or entrance of the reactor bed goes through a very rapid rise in temperature, as where the exit end remains relatively cool.
Since the effective conversion of hydrocarbon fuel is dependant upon the efficient, long-lived operation of the catalyst of the reactors, capable of thousands of startup operations, it is desirable to improve the thermal and conversion efficiency of the reactors under varying operating conditions. Thus, there is a need for a rapid uniform heating of the catalyst in a reactor system which is energy efficient.